An essential part of any optical system is a light source. A laser is an optical oscillator that consists of an active medium for amplification, a cavity formed between two mirrors and a way to partially couple light out of the cavity. FIG. 1 illustrates a laser cavity 10 in general form. The illustrated cavity 10 includes a gain medium 12, a first mirror 14, a second mirror 16, and an optical filter 18. For single mode operation, the filter 18 is configured to select among the possible cavity modes. The laser output is extracted from the cavity 10 through the mirror 16, which is partially reflective.
Lasing in silicon is challenging because of its indirect bandgap, meaning that silicon is inefficient for use as the gain medium 12. Providing light sources to silicon dies thus represents a major challenge in many areas of development, such as the development of silicon dies configured for photonics-based processing. Such dies are often referred to as “silicon photonics chips” and several solutions have been proposed in the literature for providing lasing sources to such chips, such as using off-chip external lasers, bonding III/V active material directly onto the silicon dies, or flip-chip bonding of laser dies onto the silicon dies. Example III/V materials include Gallium Arsenide (GaAs), Indium Phosphide (InP), Gallium Phosphide (GaP) and Gallium Nitride (GaN).